Random Hair Rotation
You have to enable 'Advanced' particle settings. Then a tab for the particle rotation will show up. Enable it and set 'Phase' and 'Random to 1:


Now the particles will be rotated randomly:


By default the objects will be pointing up with their y-axis and also rotate around that axis. You can play around with the 'Initail Orientation' setting and its random value to get different rotation behavior.